1. Field of the Invention
The present invention relates generally to an imaging apparatus, and more particularly, to a method for controlling a printhead to maintain a desired print quality and prevent runaway temperatures.
2. Description of the Related Art
In today's thermal inkjet industry, it is important in achieving acceptable print quality to supply a sufficient quantity of ink from an ink supply in an ink cartridge to a printhead during printing. If insufficient ink is supplied to the printhead, the printhead will print an unacceptably low quality image. This becomes very noticeable as the supply of ink in the ink cartridge approaches depletion, but is not empty. Even though sufficient ink remains in the cartridge for additional printing, the cartridge cannot be used to print acceptably, and the unit must be discarded, thus wasting the remaining ink.
The printhead must be operated at a desired operating temperature in order to ensure acceptable print quality. When the temperature is below the desired temperature, as, for example, when the printer is just switched on, the temperature may be increased by various methods. Once the printer has warmed up and is printing images, the ejection of the ink from the printhead serves to cool the printhead and prevent it from overheating. As long as the supply of ink is sufficient, the temperature of the printhead remains in the desired temperature range, and the printer achieves acceptable print quality. However, as the supply of ink drops, and insufficient ink is supplied to the printhead, the temperature can rise very quickly to unacceptable levels as the quantity of ink supplied decreases, thus experiencing a runaway temperature condition. If the printhead temperature is high enough, of course, the printhead can be ruined. Even if the high temperature does not ruin the printhead, the high temperature can significantly shorten the useful life of the printer and printhead.
It would thus be advantageous, when the ink supply drops to a low level but is not depleted, to supply sufficient ink to the printhead to maintain print quality, and prevent runaway printhead temperatures, thereby reducing the likelihood of damage to the printer.